INTERCELLULAR SECRETORY RESERVOIRS. 451 



The family of the Clusiacex'^ has especially numerous passages containing gum-resin, 

 and in fact all members of it with exception of the genus Quiina, which is separated as a 

 special group. 



According to Trecul's and van Tieghem's investigations there are in the stem and 

 roots of the true Clusiaceae three chief forms of distribution of the passages. In the 

 genus Clusia they lie only in the primary parenchyma, in the stem they occur also in the 

 pith, but are absent from the vascular bundles and the secondary cortex. 



A second category has passages in the phloem of the vascular bundles in addition to 

 the above-mentioned places; there being one in each primary phloem-group of the root- 

 bundle, in each primary bundle of the stem, and further in the secondary bast ; e. g. 

 Mammea americana : the same distribution, with the exception of those in the primary 

 bundles of the stem, is seen in Calophyllum Calaba. 



Thirdly : the passages are wanting in the cortical parenchyma of the root, but are 

 present in that of the stem, and in the primary phloem-groups and the secondary bast 

 both of the root and of the stem : Rheedia lateriflora, Xanthochymus pictorius. They 

 are present in the pith of the stem in Rheedia, but not in Xanthochymus. 



The passages run longitudinally and anastomose one with another through the whole 

 plant : more rarely in the internodes, but always, and in various individual forms described 

 by Trecul, in the nodes. From the latter, branches of tfee passages go into the petiole, 

 and through this further into the lamina. In these members they are found in most 

 species only in the parenchyma and the watery hypoderma. Only in Mammea americana 

 a number of the vascular bundles entering the petiole take the passage which traverses 

 their phloem with them out of the stem : in the case of the median bundle it goes nearly 

 to the apex of the leaf. The number of those which enter the petiole is usually high, 

 and varies according to species. Trecul states, e. g. that there are 30 in Rheedia lateri- 

 flora, about 40 in Xanthochymus pictorius, 14-20 in Calophyllum Calaba, and more than 

 200 in Clusia rosea. Their distribution in the parenchyma varies according to the species. 

 Finally, in the lamina also they run without relation to the vascular bundles, even cross- 

 ing these in certain cases, and branched here and there, but without visible anastomoses. 

 According to the arrangement in the massive leaf-substance there may be distinguished a 

 system of internal passages situated with vascular bundles in the inner chlorophyll paren- 

 chyma, and a hypodermal system, of which the passages are always narrower. For details 

 on these relations see Trecul, I.e. Of the forms investigated Mammea americana alone 

 has no passage in the lamina except that which traverses the mid-rib, but has instead a 

 round resin-containing cavity embedded in the parenchyma in each mesh of the network 

 of vascular bundles. 



Pittosporest ^. The root of Pittosporum Tobira shows originally opposite each vascular 

 plate a group of oil and resin passages of similar origin and arrangement to those in 

 the Umbelliferse, The number of the passages in each group is certainly smaller, arid 

 their arrangement often less regular than in this order : there is a central quadrangular 

 one, and usually on either side of it a smaller, triangular one. The passages in the 

 phloem-strands are absent in Pittosporum. By the same process of secondary formation 

 as in the Umbelliferse the passages are subsequently pushed outwards, under the periderm, 

 while they widen considerably, and the cells limiting them increase in number. In the 

 primary tissue of the stem there is only one passage in the outer part of the phloem of 

 each vascular bundle, and these passages of the stem are continuous with those of the 

 root at the limit of the two members. The bundles which enter the leaf are each 

 accompanied by one passage, which retains the same position as in the stem, and divides 

 in the lamina into branches, which also follow the branches of difi'erent rank of the 

 vascular bundles. 



t; 



' Meyen, Physiol. II. p. 384. — Anonymous author in Botan. Zeitg. 1846. — Trecul, in Comptes 

 Rendus, LXIII. pp. 537 and 613 (1866). — Van Tieghem, I.e. 

 ^ Miiller, I.e. — Van Tieghem, I.e. 



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